Production of metals and metal alloys of high purity

ABSTRACT

A method of making powdered metals or metal alloys of high purity wherein a monometallic or polymetallic cyanide complex is formed of a metal of Groups IIA, IIIA, IVA and IIIB of the Periodic Table of the Elements (especially or including beryllium, magnesium, aluminum, yttrium, the lanthanides elements of atomic numbers 58-71, inclusive, titanium, zirconium, hafnium, chromium, gallium, indium, thorium, cobalt and nickel). The cyanide complex is treated in crystalline form with dry hydrogen at temperatures generally between 700* and 1300*C, any hydride formed being decomposed by heating.

United States Patent 1 1 Paris et al.

1451 Sept. 30, 1975 [22] Filed: May 3. 1972 [21] Appl. No.: 250.080

[30] Foreign Application Priority Data May 6. 1971 France 71.17059 Nov. 3. 1971 France 71.40191 [52] US. Cl 75/84.1 R; 75/119; 75/121;

[56] References Cited UNITED STATES PATENTS 1.397.684 11/1921 Hahn 75/106 11/1961 Grimes 75/119 10/1967 Snyder 75/106 Primary E.\'aHli1le'l-OSCar N. Vertiz Assistant liraminer-Hoke S. Miller Attorney. Agent. or F inn-Karl F. Ross; Herbert Dubno 5 7 1 ABSTRACT A method of making powdered metals or metal alloys of high purity wherein a monometallic or polymetallic cyanide complex is formed of a metal of Groups llA. 111A. IVA and 1118 of the Periodic Table of the Elements (especially or including beryllium. magnesium. aluminum. yttrium. the lanthanides elements of atomic numbers 58-71. inclusive. titanium. zirconium. hafnium. chromium. gallium. indium. thorium. cobalt and nickel). The cyanide complex is treated in crystalline form with dry hydrogen at temperatures generally between 700 and 1300C. any hydride formed being decomposed by heating.

ll Claims. No Drawings PRODUCTION OF METALS AND METAL ALLOYS OF HIGH PURITY CROSS-REFERENCE TO RELATED APPLICATION This application relates to the commonly owned application Ser. No. 250,079 entitled NEW METAL CY- ANIDE COMPLEXES AND METHOD OF MAKING SAME.

FIELD OF THE INVENTION The present invention relates to a method of producing elemental metals or metal alloys and metal compositions of high purity. More particularly, the invention relates to a chemical procedure for obtaining refractory metals, from compounds containing same, with controlled composition at a relatively low cost.

BACKGROUND OF THE INVENTION Generally speaking metals may be obtained from their ores by processes starting with compounds such as oxides or halides of the desired metal, which are reduced chemically or electrolytically. Very electropositive metals whose compounds are therefore difficult to reduce are often treated chemically by low-cost products such as hydrogen, carbon, or carbon monoxide at a very high temperature which causes the formation of stable carbides which make it impossible to prepare sufficiently pure metals. It is therefore necessary to use chemical reducing agents which are much more expensive such as alkali metals or alkaline earths, magnesium or silicon, or to employ electrolytic reduction which uses large quantities of electricity.

The alloys of these metals are usually obtained by simultaneous fusion of the elements of the alloy when their melting points are substantially equal. When this is not the case, the less easily melted metals are dissolved in the other previously molten metals. This latter operation is usually unduly long with certain refractory metals and requires an atmosphere which is perfectly inert at the elevated temperatures required to obtain sufficiently rapid dissolution. It is also very difficult to react at high temperature a relatively volatile metal with a refractory metal and problems with contamination from the containing vessel arise.

The processes as well as the suspension furnaces which are used to prevent the alloy from reacting with the receptacle are very difficult to use and extremely expensive. In addition they are only nominally useful for large-scale industrial production of alloys. Finally this preparation of alloys by direct action of the elements requires that the individual elements themselves be prepared as powders, for the refractory metals in a high degree of purity and, in certain cases, be absolutely pure, which is once again difficult to achieve and expensive.

OBJECTS OF THE INVENTION It is therefore an object of the present invention to provide an improved method of making a metal or an alloy of high purity.

More particularly it is an object of this invention to chemically produce metals of the groups IIA, IIIA, IVA, VIA and IIIB of the Periodic Chart (shown on pages 448 and 449 of the Forty-First edition of the Handbook of Chemistry and Physics published in 1960 by the Chemical Rubber Publishing Company).

It is also an object of the present invention to provide a method of making beryllium, magnesium, aluminum, yttrium, the lanthanides (elements of atomic numbers 58 to 71 inclusive), titanium, zirconium, hafnium, chromium, gallium, indium or thorium and alloys thereof in high purity.

Another object of the invention is a chemical method of producing alloys which can be used for two or more of the above-named metals as well as binary or higher order alloys of these metals with any other metal.

DESCRIPTION OF THE INVENTION The process according to the present invention is based in principle on the reduction by hydrogen of the metal cyanide complex of the metal or the metals in question. If the cyanide complex is monometallic (i.e. containing only a single metallic element) its reduction by hydrogen yields one metal. If on the contrary the cyanide complex is polymetallic (i.e. containing several different metallic elements) its reduction yields an alloy.

Such monoand polymetallic cyanides have been described along with their methods of preparation in copending US. patent application, Ser. No. 250,079 commonly filed with this application and entitled NEW METAL CYANIDE COMPLEXES AND METHOD OF MAKING SAME.

In the case of monometallic cyanides which can be obtained preferably according to the above-named patent applications by reacting hydrocyanic acid I-ICN with a metal hydrate according to the general reaction formula:

(I) metallic hydrate(hydroxide or oxide)+hydrocyanic acid cyanide complex water The named metals are produced by reducing the cyanide complex with hydrogen according to the general reaction formula:

(II) cyanide complex-l-hydrogen metaH-hydrocyanic acid The hydrocyanic acid thus obtained, with minor losses, in reaction (II) is used again for reaction (I), making a cycle which indirectly reduces the metal hydrate (hydroxide) by hydrogen, which often is impossible to do directly. In the production of alloys, polymetallic cyanide complexes are reduced by hydrogen according to the general reaction formula:

(III) polymetallic cyanide-l-hydrogen alloy hydrocyanic acid In this case again the hydrocyanic acid which is recovered in reaction (III) can be used to obtain polymetallic cyanides.

The surprising discovery is that the reduction by hydrogen of a polymetallic cyanide complex according to reaction (III) yields an alloy in the form of a fine powder each granule of which is an alloy particle and not just a juxtaposition of granules of each of the component metals. Thus the process according to the present invention yields an alloy formed by a homogeneous phase (solid metallic solution or definite combination) or a mixture of phases conforming to that predicted by the formula. In other words the uniform alloy obtained according to the present invention has the same structure as that which is obtained by fusion and cooling of v3 the metals, with the condition, of course, that the proper thermal treatments have been carried out so that the phases appear under identical allotropic forms.

The powders so produced can be used in powder metallurgy. The production of sintered-metal bearings and like parts is facilitated by the high-purity powders according to the present invention.

The advantages which the present method has over the prior-art processes are numerous: First of all the temperatures necessary are relatively low. They range between 700 and 1300C according to the metal, which is substantially lower than the temperatures necessary for the prior-art methods. It is also much easier to avoid reaction with the receptacles at these temperatures, and purer products are obtained.

ln the case of refractory metals and alloys the cyanide reduction process according to the present invention yields a powder whose granule size is dependent on the final temperature and also on how long this temperature is maintained. This means that metallic materials can be produced which are particularly adapted to sintering.

The economical advantages inherent in the present invention are a result of using hydrogen as reducing agent, hydrogen being particularly inexpensive and of avoiding preparation of the constituent elements of the alloy individually, this operation being often very difficult and expensive when the metals are refractory or very reactive, as the metals of the lanthanum series.

The conditions under which the operationsof the present invention are carried out depend on the metal or the alloy to be made. This process includes, however, some basic steps:

1. Formation of the metal cyanide complex The crystals of the cyanide metal complex which are to be reduced with hydrogen in order to obtain a metal or a metallic alloy are prepared according to the methods described in the above-mentioned commonly filed patent applications.

According to the principles set forth in our copending application Ser. No. 250,079 and identified more fully above, the metal complex may be formed by two main process sequences, whether the complex is of the monometallic type or of the polymetallic type.

Thus the complex may be produced by treating a basic compound of a metal M or of several metals (M, M, M". as a simple compound. a mixed-metal compound, a coprecipitate of metals compounds, a mixture of precipitates of the metal compounds or a compound containing two or more of the metals, and preferably in the form of the oxide, hydroxide, carbonate or salts which can be considered weakly basic, with a complex acid having the general formula H, [M (CN) where M represents the same metal as that of the basic compound in the case of a monometallic complex or a different metal in the case of a polymetallic complex. x represents the coordination number of the Metal M, and y and p are determined by the ionic valances of the portion of the molecule in square brackets. This neutralization reaction produces either the polymetallic complex or the monometallic complex of which examples have been given below.

The complex acid may be formed, on the one hand by ion-exchange principles and, on the other hand, by ionic displacement methods. In accordance with the ion-exchange technique, an acid ion-exchange resin may be prepared and a solution of an alkali-metal (e.g. potassium) salt of the complex anion may be passed therethrough so that hydrogen ion exchanges for potassium ion and the acid appears in the eluate. Of course, anion-exhange resins may be used whereby the resin is charged with the complex anion and is eluted with an acid whose anion exchanges for the complex anion so that again the complex acid appears in the eluate.

In the second technique, a displacement method is used whereby, for example, a barium salt of the complex anion is reacted in aqueous solution with sulfuric acid to precipitate barium sulfate and leave complex acid in solution. The barium salt of the complex may be produced, in turn, by reacting the metal sulfate with barium cyanide to precipitate barium sulfate and leave the barium cyanide complex in solution.

When the complex acid is reacted with the basic compound by forming the complex acid in situ, i.e. by reacting HCN with the hydroxide, oxide, carbonate etc. of the metal to be found in a monometallic complex, the hydrocyanic acid is used in a concentration of 10 to 60% by weight and in excess over the basic compound by lO to 20%. The use of the previously prepared complex acid requires a predetermined quantity according to the stoichiometry. It is important to observethat the solution containing the metal-metal cyanide complex should have the metals in their desired proportions in the alloy to be produced and, therefore, in the desired proportions in the cyrstalline product.

The crystals are formed preferably by low temperature removal of the water from the solution and we may use vacuum evaporation at temperatures up to, say, 60C or removing the water by azeotropic distillation under reducedtemperatures up to 40C. A suitable azeotropic .entrainer for this purpose is gasoline.

2. Reductionof the Metal Cyanide Complex The crystals of the metal cyanide complex are first dried in a pure and dry hydrogen atmosphere or under a vacuum at 200C. Then they are reduced by dry and pure hydrogen passed over or through them at a rate between 2 liters per hour to 10 liters per hour (l/H) at temperatures between 700 and 1300C. The metal or thealloy yielded by this reduction of the complex is recovered depending on its fusion temperature and the temperature of the end of the reduction as a liquid or as a powder.

In the case of a metal such as zirconium it is necessary to bring the temperature at the end of the reduction to at least l200C to eliminate the intermediate hydride which has formed. ln the case of thorium whose hydride is even more stable, it is absolutely necessary to follow up the reduction treatment with a heating under vacuum (10' bar) at 1 C in order to decompose the hydride and yield the metal. The drying temperature may be in the range of l50 to 250C.

in this reduction operation the hydrogen in excess to that needed for the reduction of the solid carries off the hydrocyanic acid formed. This latter product is extracted by scrubbing with water, thereby obtaining a solution which can be used again for the preparation of the starting cyanide complexes. The hydrogen after drying is recycled to the apparatus for reducing the complex after the quantity of hydrogen lost in the reduction reaction is added back to it.

SPECIFIC EXAMPLES Example I. Magnesium The tetracyanomagnesiate of magnesium Mgl Mg(CN is prepared according to the method described in Example l of the above-mentioned patent application.

The crystals of this cyanide complex are first dried under a stream of pure and dry hydrogen at 200C and then, still with this same hydrogen stream. the temperature is raised at a rate of 600C per hour (C/h) to lO00C.

Under these conditions the residue of this reduction is melted metallic magnesium which solidifies into a completely homogeneous ingot.

Example ll. Beryllium The tetracyanoberyllate of beryllium: Be[Be(CN) is prepared as in Example ll of the above mentioned patent application. The crystals of this cyanide complex are first dried under a stream of pure and dry hydrogen for several hours at 200C then, still with this same hydrogen stream, the temperature is raised at 600C/h to ll00C. This yields a powder of metallic beryllium.

Example lll. Aluminum l. Formation of an aqueous solution of the hyxacyanoaluminate of aluminum:

A suspension of an aluminum hydroxide gel or of a fine hydrargyllite resulting from the hydrolysis of a solution of sodium aluminate obtained by alkali solubilization of bauxite according to the Bayer process is filtered. The hydrate cake is carefully washed then introduced into an autoclave with an aqueous solution of hydrocyanic acid whose concentration by weight lies between l0 and 40% HCN. In order to dissolve the hydrate quickly an excess of from l0 to of hydrocyanic acid relative to the quantity theoretically necessary for reaction (I) is employed. A mixer is used to agitate the mixture energetically and the sutoclave is heated to a temperature between 80 and l50C according to the reactivity of the hydrate, the attack on a gel using a lower temperature than that upon a wall crystallized hydrate.

Once all the hydrate is transformed into a soluble cyanide complex the excess hydrocyanic acid is degased and recovered and the aqueous solution is removed from the autoclave in order to perform the following operation.

2. Isolation of the hexacyanoaluminate of aluminum:

The aqueous solution of the cyanide complex can be concentrated by evaporation in a vacuum between 40 and 6020 C. The resulting crystals are subsequently dried in a vacuum. It is faster to perform an azectropic removal of the water with a nonmiscible liquid having a low boiling point, gasoline for example. This azeotropic distillation carried out under reduced pressure allows rapid recovery of the crystals of the cyanide complex without raising the temperature above 20 to 40C.

3. Reduction of the hexacyanoaluminate of aluminum:

The completely dry crystals of the cyanide complex are subjected to progressively higher temperatures in a stream of pure and dry hydrogen injected at from 2 l/h to 10 l/h until a final temperature lying between 700 and 900C is attained. The reduction of the complex starts at around 400C. but only is rapid between 600 and 800C. Since the final temperatures of the reduction treatment is fixed above 700C melted aluminum is recovered which makes its extraction from the apparatus very easy. The metallic powder obtained in effect when the reduction is carried out below the fusion point of aluminum is very finely divided and very oxidizable.

The excess hydrogen not used in reduction carries off the hydrocyanide acid formed. This produce is extracted from the hydrogen by scrubbing with water thereby obtaining a hydrocyanic acid solution which can be used for attacking the hydrated alumina. The hydrogen is dried and recycled to the apparatus where the reduction is effected after admixing with a quantity to make up for that lost during reaction (ll).

Example lV. Chromium Powder The hexacyanochromate of chromium (lll): Ca[Cr(CN) l is prepared according to the method of Example III of the above-described copending patent application.

The crystals of this cyanide complex are first dried for several hours in a stream of dry and pure hydrogen at 200C. Thereafter, still with this same hydrogen stream, the temperature is raised at 600C/h to 700C This yields a powder of metallic chromium.

Example V. Titanium The octacyanotitanate of titanium (lV Ti[Ti(CN ),.l is first prepared according to Example V of the abovenamed copending application. The crystals of this cya nide complex are first dried in a stream of pure and dry hydrogen at 200C for several hours. then, still with this same hydrogen stream, the temperature is raised 600C /h to lO00C and this latter temperature is maintained for 4 to 5 hours. This yields a hydrided titanium powder which can be subjected to a vacuum of 10 bar at l00OC to yield the pure metal.

Example Vl. Metallic zirconium The octacyanozirconatc of zirconium (lV ZrlZrtCN is first prepared according to the method of Example VI of the above-named copending patent application. The crystals of this cyanide complex are first dried as described in Example V of this application and then the temperature is raised, still with this same hydrogen stream, at 600C/h to l200C. This latter temperature is held for 4 to 5 hours. The intermediate hydride so produced loses its hydrogen and becomes a fine powder of metallic zirconium.

Example Vll. Thorium The octacyanothorate of thorium: Th[Th(CN)xl is first prepared according to Example Vll of the previously cited application. The crystals of this cyanide complex are dried and their temperature is raised as in Example VI of this application to l200C. This produces a thorium hydride which when subjected to a vacuum of l0 bar at l l00C yields the metal.

Example Vlll-Production of a Metal of the Lanthanide Group (Elements of Atomic Numbers 57-71 or of Yttrium Gadolinium will be employed here for illustration but the method given below is equally applicable to any of the metals of the lanthanide group or yttrium. The hexacyanogadolinate of gadolinium Gd[Gd(CN).-.l is first prepared according to Example VIII of the above-cited commonlyassigned patent application. This complex is dried and heated as described in Example VI of this application to a temperature of lOOO C. The yield is a powder of metallic gadolinium Example IX. Production of an Alloy of Cobalt and Samarium SmCo Whose Magnetic Properties are Well Known for Use in Permanent Magnets The method described immediately below is equally applicable to other alloys of cobalt with any other lanthanide in any other proportion.

The bimetallic cyanide complex having the formula H ,Sm[Co'(CN) is prepared according to the method of Example X of the above-cited application.

The crystals of this cyanide complex are dried with hydrogen and their temperature is raised as in Example VI to l250C. The reduction of the complex starts at around 750C and stops at between l000 and 1 100C, but the powder of alloy SmCo is then too oxidizable so that the temperature is raised to between 1250" and l300C under hydrogen in order to agglomerate the granules of the powder by slight sintering to obtain a less oxidizable alloy.

Example X. Production of Nickel-neodymium NdNi This method is equallyusable to produce alloys of nickel with any other lanthanide or with yttrium in other proportions.

The bimetallic cyanide complex having formula H,Nd[Ni(CN) is prepared according to the method described in Example XI of the above-cited commonly assigned patent application.

The crystals of this cyanide complex are reduced exactly as in Example IX of this application to produce an alloy powder NdNi Example X1. Chromium-yttrium YCr This method is equally applicable for alloys of chromium with the other lanthanides or yttrium in other proportions.

The bimetallic cyanide complex Y{Cr(CN)] is pro duced according to the method of Example XII of the above-cited copending application.

The crystals of this complex are treated exactly as described in Example lX above to yield a powder YCr.

Example Xll. Lanthanum-yttrium LaY This method is equally applicable for any alloy containing two or more lanthanide elements or lanthanide elements alloyed with yttrium in the corresponding proportions.

The bimetallic cyanide complex of formula La- [Y(CN).;] is prepared according to the method of Example Xlll of the above-cited copending patent application.

The crystals of this cyanide complex are then reduced by hydrogen under the same conditions as given in Example VIII of this application to yield a powder of lanthanum-yttrium alloy LaY.

Example Xlll. Lanthanum-aluminum LaAl This method is equally applicable to the preparation of alloys of aluminum with any other lanthamide or yttrium in the proportions corresponding to those of the respective alloys.

The bimetallic cyanide complex of formula Al[- La(CN)6] is prepared according to the method of Example XlV of the simultaneously filed above-cited patent application.

The crystals of this cyanide complex are thereafter reduced with hydrogen according to the same method employed in Example VIII of the present application to yield LaAl.

Example XIV. Production of Cobalt-samariumbarium smBa Co The 'trimetallie dyanide complex having formula SmBaO, I-l ,g[Co(CN) ]5 is prepared according to the method described in Example XV of the above-cited commonly assigned patent application.

The crystals of this cyanide complex are then reduced with hydrogen under the same conditions as those of Example IX of this application and thereby yield a powder of the ternary alloy having a composition corresponding to the formula SmBl Co Example XV. Production of Cobalt-samarium-neodyniumproseodymium Alloy o.s o.2s 0.25 s

The polymetallic cyanide complex having the formula Sm Nd ,,Pr., H, [Co(CN) l is prepared according to the method described in Example XVI of the above-cited application.

The method of Example lX above is employed to yield an alloy powder having a composition of the formula u.s o.-zs o.2s s- It is possible and within the scope of the present invention to use the same or similar process for any alloy of cobalt containing other lanthanides of yttrium in the various proportions corresponding to the alloy composition.

We claim:

1. A process for producing a metal or a metal alloy consisting essentially of the steps of forming a cyanide complex of at least one metal selected from the group which consists of beryllium, magnesium, aluminum, yttrium. lanthanide elements of atomic numbers 58 to 71 inclusive, zirconium, hafnium, chromium, gallium, indium, cobalt and nickel, said cyanide complex being formed by crystallizing it from an aqueous solution of ions of its components, and drying the crystals thus formed under vacuum or in a stream of hydrogen at a temperature of to 250C; and reducing said cyav nide complex with dry gaseous hydrogen at a temperature 700 to 1300C.

2. The process defined in claim 1 wherein said complex is monometallic.

3. The process defined in claim 1 wherein said complex is polymetallic.

4. The process defined in claim 1 wherein said cyanide complex is formed by treating with an aqueous solution of hydrocyanic acid, a hydrate of the metal.

5. The process defined in claim 1 wherein the temperature of said crystals is raised from the drying temperature to the reducing temperature at a rate of about 600C per hour.

6. The process defined in claim 5 wherein the dry crystals are exposed to a stream of hydrogen for a period of at least 3 hours.

7. The process defined in claim 6 wherein reduction of the crystals is carried out at a temperature below the melting point of the metal recovered.

8. The process defined in claim 1 wherein said crystals are produced by:

A. reacting an aqueous solution containing 10 to 60% by weight of hydrogen cyanide with a basic compound of at least one metal and selected from the group which consists of the hydroxides, oxides and carbonates of the metal alone or in association with the corresponding compounds of another metal;

B. recovering an aqueous solution containing a metal-metal cyanide complex from step (A); and

C. recovering crystals of said metal-metal cyanide complex from the solution in step (B) by heating said solution at a temperature below 60C under vacuum to evaporate water.

9. The process defined in claim 1 wherein said crystals are produced by:

A. preparing an acid metal-cyanide complex in aqueous solution and reacting said acid with a metal hydroxide, oxide or carbonate;

B. recovering an aqueous solution containing a metal-metal cyanide complex from step (A); and

C. recovering crystals of said metal-metal cyanide complex from the solution in step (B) by heating said solution at a temperature below 60C under vacuum to evaporate water.

10. The process defined in claim 1 wherein said crystals are produced by:

A. reacting an aqueous solution containing 10 to 60% by weight of hydrogen cyanide with a basic compound of at least one metal and selected from the group which consists of the hydroxides, oxides and carbonates of the metal alone or in association with the corresponding compounds of another metal;

B. recovering an aqueous solution containing a metal-metal cyanide complex from step (A); and

C. recovering crystals of said metal-metal cyanide complex from the solution in step (B) by azeotropically distilling water from said solution at a temperature of at most 40C and at reduced pressure with an azeotropic entrainer.

11. A process for producing a metal or a metal alloy consisting essentially of the steps of forming a cyanide complex of at least one metal selected from the group which consists of titanium and thorium, said cyanide complex being formed by crystallizing it from an aqueous solution of ions of its components, and drying the crystals thus formed under vacuum or in a stream of hydrogen at a temperature of 150 to 250C; and reducing said cyanide complex with dry gaseous hydrogen at a temperature of 700 to l300C, the reduction being followed by heating to lOO0 and 1 C respectively at a vacuum of 10' torr. 

1. A PROCESS FOR PRODUCING A METAL OR METAL ALLOY CONSISTING ESSENTIALLY OF THE STEPS OF FORMING A CYANIDE COMPLEX OF AT LEAST ONE METAL SELECTED FROM THE GROUP WHICH CONSISTS OF BERYLLIUM, MAGNESIUM, ALUMINUM, YTTRIUM, LANTHANIDE ELEMENTS OF ATOMIC NUMBERS 58 TO 71 INCLUSIVE, ZIRCONIUM, HAFNIUM, CHORMIUM, GALLIUM, INDIUM, COBALT AND NICKEL, SAID CYANIDE COMPLEX BEING FORMED BY CRYSTALLIZING IT FROM AN AQUEOUS SOLUTION OF IONS OF ITS COMPONENTS, AND DRYING THE CRYSTALS THUS FORMED UNDER VACCUM OR IN A STREAM OF HYDROGEN AT A TEMPERATURE OF 150* TO 250*C, AND REDUCING SAID CYANIDE COMPLEX WITH A DRY GASEOUS HYDROGEN AT A TEMPERATURE 700* TO 1300*C.
 2. The process defined in claim 1 wherein said complex is monometallic.
 3. The process defined in claim 1 wherein said complex is polymetallic.
 4. The process defined in claim 1 wherein said cyanide complex is formed by treating with an aqueous solution of hydrocyanic acid, a hydrate of the metal.
 5. The process defined in claim 1 wherein the temperature of said crystals is raised from the drying temperature to the reducing temperature at a rate of about 600*C per hour.
 6. The process defined in claim 5 wherein the dry crystals are exposed to a stream of hydrogen for a period of at least 3 hours.
 7. The process defined in claim 6 wherein reduction of the crystals is carried out at a temperature below the melting point of the metal recovered.
 8. The process defined in claim 1 wherein said crystals are produced by: A. reacting an aqueous solution containing 10 to 60% by weight of hydrogen cyanide with a basic compound of at least one metal and selected from the group which consists of the hydroxides, oxides and carbonates of the metal alone or in association with the corresponding compounds of another metal; B. recovering an aqueous solution containing a metal-metal cyanide complEx from step (A); and C. recovering crystals of said metal-metal cyanide complex from the solution in step (B) by heating said solution at a temperature below 60*C under vacuum to evaporate water.
 9. The process defined in claim 1 wherein said crystals are produced by: A. preparing an acid metal-cyanide complex in aqueous solution and reacting said acid with a metal hydroxide, oxide or carbonate; B. recovering an aqueous solution containing a metal-metal cyanide complex from step (A); and C. recovering crystals of said metal-metal cyanide complex from the solution in step (B) by heating said solution at a temperature below 60*C under vacuum to evaporate water.
 10. The process defined in claim 1 wherein said crystals are produced by: A. reacting an aqueous solution containing 10 to 60% by weight of hydrogen cyanide with a basic compound of at least one metal and selected from the group which consists of the hydroxides, oxides and carbonates of the metal alone or in association with the corresponding compounds of another metal; B. recovering an aqueous solution containing a metal-metal cyanide complex from step (A); and C. recovering crystals of said metal-metal cyanide complex from the solution in step (B) by azeotropically distilling water from said solution at a temperature of at most 40*C and at reduced pressure with an azeotropic entrainer.
 11. A process for producing a metal or a metal alloy consisting essentially of the steps of forming a cyanide complex of at least one metal selected from the group which consists of titanium and thorium, said cyanide complex being formed by crystallizing it from an aqueous solution of ions of its components, and drying the crystals thus formed under vacuum or in a stream of hydrogen at a temperature of 150* to 250*C; and reducing said cyanide complex with dry gaseous hydrogen at a temperature of 700* to 1300*C, the reduction being followed by heating to 1000* and 1100*C respectively at a vacuum of 10 4 torr. 